With a display device including a backlight, the technique of dividing a display surface into a plurality of areas and on-off controlling light from the backlight according to areas is known. With a side light source type backlight a scattering material is mixed into a transparent resin material to form a light guide member. Light from a light source disposed at a side is scattered by the light guide member. With a backlight having this structure, the backlight is divided into areas parallel with a direction in which light from each light source travels, and light sources disposed according to the areas are on-off controlled. Because light from a light source corresponding to another area is not utilized, light emission efficiency decreases.
In recent years backlights including polymer dispersed liquid crystal (PDLC) as a light guide body have been known. With the PDLC, switching between a scattering state in which incident light is scattered and a transmission state in which incident light is transmitted is performed by controlling a voltage applied to area electrodes. With a backlight including the PDLC, control is exercised so that the PDLC will be in the scattering state. By doing so, light emitted from a side light source is emitted toward a display surface. For example, area electrodes are formed according to areas formed in a direction intersecting a direction in which light from a light source travels, and switching is performed between the scattering state and the transmission state of the PDLC. By doing so, backlight light is controlled according to the areas. With a display device using PDLC, divided areas are formed in a direction intersecting a direction in which light travels. Therefore, backlight light is controlled according to the divided areas in a state in which a light source is always on.
See, for example, Japanese Laid-open Patent Publication No. 2014-102295.
However, if areas are formed in a display device in a direction intersecting a direction in which light from a light source travels, the distance from the light source differs among different areas. Therefore, as the distance between the light source and an area becomes longer, the intensity of light which enters the area decreases. As a result, if an electrode is driven uniformly in each area, the luminance of an area more distant from the light source becomes lower. However, if luminance control is exercised with an area whose luminance is lowest as reference, the luminance of an entire backlight decreases.